Copper nitrate hydrate

Poly(2-ethyl-2-oxazoline) (POZ) and copper nitrate hydrate (Cu(NO₃)₂·xH₂O) were purchased from Sigma-Aldrich and used without further purification.

Copper nitrate hydrate (99.999% Cu(NO₃)₂), sodium hydroxide (10.0 N standardized solution, NaOH), sodium hydroxide (pearl, 97% NaOH), and Cu foil (thickness: 0.025 mm, 99.999%) were purchased from Sigma Aldrich, Saint Louis, MO, USA. Hydrazine solution (35 wt% in H₂O, N₂H₄) was purchased from Alfa Aesar, Heverville, MA, USA. These materials were used for the Cu-NW synthesis. Iron (Fe) nanoparticles (99.5+%, 30 nm, Fe₂O₃ alpha) were used as a catalyst for the CNT growth, and were purchased from RND Korea, Ltd, Gwangmyeong, Korea. A silver nanowire (Ag-NW) solution was purchased from Duksan Hi-Metal (Ulsan, Korea), and graphene oxide (GO) was purchased from Grapheneall, Ltd, Siheung, Korea. Nafion-117 and 20 wt% Nafion solution were purchased from the DuPont Company (Midland, MI, US), and were used as the ionic polymer membrane of the IPMC and the interface material with the Cu-NW, respectively. The cation used for the actuation of the IPMC in the Nafion was 1-Ethyl-3 methylimidazolium trifluoromethylsulfonate (EMIM-Otf, ionic liquid), and this was purchased from Merck KGaA (Darmstadt, Germany). Polyvinylidene difluoride (PVDF) membrane filter paper (pore size: 0.20 μm, diameter: ϕ47 mm) was purchased from Hyundai Micro., Ltd, Seongnam, Korea, and was used for Cu-NW synthesis and fabrication of the GO/Ag-NW paper electrode.